wl: Fix unused_imports and dead_code warnings
wl: Fix unused_imports and dead_code warnings

These functions are only used when the gpu feature is enabled.

BUG=none
TEST=`cargo build` and see no warnings

Change-Id: I8c354b0122032a6d6c57d16837d9d9e857ac03c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2891122
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>
Reviewed-by: Keiichi Watanabe <815e4e8f7c92a23424d7c3f51ead622bcedbc720@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm